Maybe Wall Street thinks Google should get a discount for its reported offer to purchase Groupon.
Shares of the online search giant fell as much as 3.9 percent Tuesday amid news that it is seeking to buy the discount shopping web site for $6 billion.

Google shares (NASDAQ: GOOG) were trading at 560.62 mid-afternoon Tuesday, down 21.49, or 3.7 percent, from Monday's closing price of 582.11. Earlier Tuesday, Google slipped as low as 559.23.
For a company with a market valuation of $140 billion and more than $33 billion in liquid assets, $6 billion might not seem like crazy money, especially given the buzz that Groupon has been generating. But it's still almost twice as much as Google paid for online advertising company DoubleClick three years ago and would be Google's most expensive acquisition to date.
Over the past decade, Google has made more than 80 acquisitions. Other than DoubleClick, the only buyout that cost Google more than a billion dollars was YouTube, which the company bought for $1.65 billion in 2006.
Google also bought a 5 percent stake in AOL for $1 billion in 2006, selling it back to Time Warner last year for $283 million. Smooth.
Wall Street's real issue with the Google's rumored offer, however, is that Groupon was valued at only $1.35 billion last April. Investors likely are skeptical that Groupon's value has more than tripled in the past seven months.
Groupon, based in Chicago, was founded in November 2008 and is projected to generate $500 million in revenue this year. Groupon currently is in more than 250 markets worldwide. It reportedly has more than 20 million subscribers, who are offered "deals of the day" from local merchants.

Chris Nerney writes about the business side of technology market strategies and trends, legal issues, leadership changes, mergers, venture capital, IPOs and technology stocks. Follow him on Twitter @ChrisNerney.